An anti-slip assembly for a staple gun has a mounting device, an operating device and a limiting device. The mounting device is formed in the staple gun and has a mounting recess, a positioning recess, a pivotal recess and a through hole. The operating device is movably connected to the mounting device and has an anti-slip arm and an operating cap. The anti-slip arm is rotatably mounted in the mounting recess and has a mounting rod, a spring, a pivotal rod and an abutting stem. The operating cap is movably mounted in the mounting recess, is mounted around the anti-slip arm and has a releasing recess, a pressing recess, a pushing protrusion and at least one holding flange. The limiting device is detachably connected to mounting device and the staple gun and has a limiting frame and a limiting panel.